i had a testpipe mated up to a large diameter exhaust on my crx. it was mad loud and it also smelled a little bit. since my o2 sensor comes before my cat (b16), i dont have the ecu problem and im also running stock ex. manifold. ive heard hondas need some back pressure or else power can actually decrease. i switched to a gutted cat from a testpipe. belive it or not, the sound was cut down a lot, no more backfiring, and no more smell (almost).